childbirth can cause a change.
what your wife can do and this will work because it worked for me and someone else i gave this advice to.
tell her to do kegle exercises, this is when she pretend she is stopping the flow of her urine, and then let it go. if she can do at lease 10 of these a day her vagina will feel tighter.
she has to keep up with it, because when i stop doing it my b/f knew.